Foreign-potential-detecting device



Patented Nev. 4i, i224.

UNITE WILLIAM H. Yllffll;R'lN, OF NEW YORK, N. Y., ASSGNOR TO TLPHONE AND TELEGRAPH COMPANY, A CORPORATON 0F NEW YORK.

FOREIGN-POTENTIAL-DETECTING DEVICE.

application nieu January l5, 192i. serial No. 435.150. i

Toy all whom t may concern.' y

Be it known that I, lVILLIAM MAnrIN, residing at New York, in the county of Bronx and State of New York, have invented certain Improvements in Foreign flotential Detecting Devices, of which the following is a Spescation.

This invention relates to electrical testing devices and especially to an arrangement for determining the presence of foreign potentials upon a signaling circuit, such as a telephone subscribers line circuit.

As is well known, various arrangements have been devised and used for the secret overhearing of conversations. Certain of these involve the use of the transmitter of a telephone subscribers set which, whenthe receiver is on the hoolr, may be energized by means of a source of foreign potential, that is, some source other than that which is applied to the telephone line yat the central oice, so that thev said transmitter is adapted to transmit any sounds that may fall thereon to a receiver connected with what may be ter-n1- ed the overbearing circuit and thereby the sound-s will be overheard. It is sometimescustomary to providesuch overbearing circuit with al switch whereby the said circuit may be opened andthe source of foreignpotential may be removedv fromr the transmitter when the telephone subscriber attempts to use his telephone for the purpose of receiving or making a call. It may be readily seen that such an overbearing or detecting device maybe installed upon a telephone set without the' knowledge of the telephone subscri-ber and also without the knowledge of the company operating the telephone line.

It is the object of this invention to provide a simple and effective arrangement for detecting the presence of such foreign potentials upon a telephone circuit without visiting the subscriber and also to prevent the subscriber from detecting that his line is being tested by the telephone company for the presence of such foreign potential.

This invention will be better understood from the following description when read in connection with the attached drawing which shows one from of embodiment of the said invention.

In the drawing, a subscribers telephone set 1 is connected by means of the line wires 2 with the switchboard, located in the telephone oflice, terminating therein in a jack 3. The telephone set, which is indicated scheother winding of which 15 is connected withl y the receiver 16 by means of which sounds t impressed upon the transmitter 7 may be overheard. The conductors 2 terminate upon the contact 17 of the main` distributing frame in the terminal room of the central office. This line would normally be cross-connected at the main distributing` frame to thel contacts 18 and would extend thence through the intermediate distribiliting frame to the jack 3 at the switchboard. However, when such line is under observation and `test. for the existence of foreign potentials thereon, the crossconnection at the main distributing frame is opened and the said line is looped through the circuit indicated at A. l The in'- sertion of this circuit between the subscribers line and the switchboard may be effected by the use of specially designed plugs, which are inserted at the main frame in place of the heat coils and also by placing a connector upon the sleeve contact of the intermediate distributing frame, thereby connecting the conductor 19 tothe sleeve contact, the pnrn pose of which connection willv be made clear hereafter.

The circuit A comprises the relays 20, 21, 22 and 23, which are designed to control automatically the apparatus for determining the presence of a foreign potential land, also to effect the signaling of the operator whereby the 'normal operationsmayl be carried on. Connected with the circuit A is a battery B2, which is designed to furnish the current to operate the relays of the circit A. rllie determination of the` presence and the magnitude of a foreign potential may be made either by means of a milliameter 24 or by means of a buzzer 25, which is controlled by means of a relay 26. Message registers 27 and 28 are also associated with the circuit for the purpose of registering the number` of calls, the manner of doing which will be made clear later. l A resistance R, is intended kto be bridgedl across the circuit to the switchboard tsl in order to operate the line relay (not shown) and thereby to give a signal to the operator. associated with the jack 3 at the switchboard is a plug 29 ot a cord circuit, which may be of any well known subscriber type.

Having in mind the foregoing description 'of the various parts of this apparatus, the invention will be clearly understood trom the following description of its mode of operation.

Let it be assumed that the receiver 6 at the subscribers station l is upon its hool, and that the switch is open, so that no current will flow from the battery B2 at the central orifice over the said line. Let it also be assumed that the switch l2 at what may be termed the listening point, is closed, so that current flows from the battery B1 through the transmitter 7 and the winding 13 of transformer 14. Any sounds, theretore, that might tall upon the diaphragm et the transmitter 7 may be heard by means et the receiver 16. Having in mind this situation, let it now be assumed that the subscriber at station l, desiring to make a call, removes his receiver trom the switch 9. The operation ot the hoolr switch closes the lino circuit through the winding 5 and transmitter 7, thereby allowing current to How trom the battery B2 at the central orlice over conductors 30 and 3l, Winding or relay 2O7 contact 83 of relay 2l, contact of relay 22, conductor 35 to and through the subscriberis set and thence through conductor 36, contacts 37 and 38 respectively of relays 22 and 2l and conductor 39 to the grounded side of the battery B2. Relay 2O will be operated by the flow of current through winding 32 and will close its contact 40. rlhis operates message register 28 and also allows the current to flow over a circuit from battery B2, conductor 3l, contact 40, conductor 4l, contact 42 of relay 22 and through the winding 43 ot relay 2O and the winding of relay 2 and conductor 39 ot the grounded side ot battery B2. rilhis causes relay 2O to be locked up and also results in the operation ot relay 21, thereby opening contacts 33 and 88 and closing contacts 44 and 45. By the opening ot contacts 33 and 38 the battery B2 is removed from the line circuit and remains disconnected therefrom so long as relay 2l is operated. The removal of this battery from the line circuit is necessary in order to enable the detection and measurement of any foreign potential on the said line circuit. By the closing of contact 44, a circuit is established from the said con tact through a meter connected with the switch 47, conductor 46 over the upper line conductor and through the winding and the transmitter 7 (across which is bridged the source or' potential El), thence over the lower line conductor to conductor 35, conwiegen tact 46 ot relay 22, to contact 44 of relay 2l. if it is assumed that the switch 47 is operated toward the right, the circuit 'just traced will be connected through the ammeter 24. Consequently the battery B1 at the listening point which is bridged across the transmitter 7, is also in effect bridged across the said ammeter and consequently the presence of the said) battery will be made known and the magnitude of the current will be determined. An alternative method for the detection of the foreign potential, which comprises the use ot a relay 26, a. buzzer 25 and a message register 27, is also shown. It, for example, the switch 47 were operated toward the left, the battery B1 would cause a iiow o'lcurrent through the winding ot the polarized relay 26 to operate the buzzer 25 and also the message register' 27, which are connected in parallel across the source of current B2. Message register 27 counts how often the buzzer rings. The reading et it in connection with the reading on message register 28, which registers the number' ot calls made by the subscriber, indicates on how many occasions when the subscriber called, the 'foreign potential was on the line.

Simultaneous with the act ot detecting the presence and the magnitude ot the foreign potential, the relay 2l through the closing ot its contact 45, closes a circuit through the resistance R1 and the conductors 49 which causes the operation of line relay and the glowing of a signal at the switchboard. YUpon the receipt of this signal the operator inserts the plug 29 of the cord circuit in the jack 3, thereby permitting the current to flow over the sleeve contact of the said jack, and over conductor 19 which, as stated heretotore, was connected with the sleeve contact at the intermediate distributing frame by means or" a suitable connector and thence through relay 23 to ground. rlhis causes the operation of relay 23 which by the closing et its contact, in turn causes the operation oli' relay When the relay 22 operates, contacts 234, 37', 42 and 46 are opened and con tacts and 5l are closed. The etl'ect oif the opening and ol" the closingl of the said contacts is to disconnect the apparatus of the testing circuit from the line circuit and to connect the line circuit over the said contacts 50 and 5l, directly with the circuit at the switchboard.

Relay 22 is so designed thatwhen energized its outer contacts 42 and 46 open before contacts 50 and 5l close, thereby removing the testing apparatus or the testing circuit trom the line circuit and releasing relays 20 and 2l before connecting the subscribers line circuit through to the switchboard in the normal way. Current tor talking over the subscribers line circuit is then supplied in the normal way over the cord Ll U lll)

circuit from the central office battery. lVhen the operator removes the plug from the jack at the switchboard relay 23 is de-energized thereby which in turn releases relay 22 and the system is restored to its initial condition. If, on the other hand, the operator desires to call the subscriber, the insertion of the plug in the jack 3 will energize relays 23 and 22 and thereby connect the operator with the subscriber.

It will be seen that this arrangement provides means for momentarily disconnecting the central oiiice battery from the subscribers line circuit when the subscriber removes his receiver from its hook, and connecting during that period of time across the said line circuit a device sensitive to direct current, whereby any abnormal source of direct current potential which may be connected with the said line circuit may be detected. There is always a small interval of time after the operation of the line relay and the flashing of a signal at the switchboard until the operator answers the call by inserting plug 29 of the cord circuit into the line jack .3. This time is suiiicient for the indication of the foreign current by some sensitive detecting device. Then plug 29 of the cord circuit has been inserted, the subscribers line circuit is automatically connected through to the switchboard so that the call may be handled in the normal way. The circuit furthermore, provides means for automatically disconnecting the detecting devices and their controlling relays from the subscribers circuit when 'the said circuit is connected through to the switchboard for normal talking purposes.

Although this invention has been disclosed as embodied in the particular form, it is apparent that it is capable of embodiment in other and different forms, without departing from the spirit and scope of the appended claims.

What is claimed is:

l. In a signaling system., Athe combination with a telephone subscribers line of a source of foreign potential having means to impress it across the said line only when the said subscribers line is in operating condition, a telephone switchboard and means to automatically show the presence of such foreign potential and to effectively connect said line to said switchboard.

2. In a signaling system the combination with a telephone subscribers line circuit of a source of potential normally foreign to the said circuit having means to effectively connect it thereto, a testing circuit connected with the said line circuit arranged to indicate the presence of the said foreign potential whenever a call originates upon said line circuit and means to automatically operate the line signal after a test has been made.

3. In signaling system, the combination with a line circuit having its transmitting device normally disconnected therefrom, means foreign to the said line circuit designed to energize the said transmitting device and arranged to be disconnected therefrom, and indicating means arranged to be connected automatically with the said line circuit to show the presence of the said foreign energization means when the said transmitting device is effectively connected with the said line circuit.

4. In a signaling system, the combination with a telephone subscribers line circuit having a microphone associated therewith, but normally effectively disconnected therefrom, a listening circuit comprising a source of potential and an indicating instrument having means to bridge it across the said microphone, and testing neans having means for its automatic connection with the said line circuit whenever the said microphone is effectively connected thereto in oider to originate a call upon said line circuit. l

5. In a signaling system, the combination with a telephone line having a substation set connected thereto, of a source of foreign potential, having means to bridge it across the transmitter of the/ said substation set, and current indicating means having means for its automatic connection with the said line circuit by the operation of the hook switch of the said substation set, to indicate the presence of the source of foreign potential across said transmitter.

6. In a signaling system, the combination with a telephone subscribers line adapted to have a potential impressed thereon from a source normally foreign to the said subscribers line, a testing circuit inserted in the said subscribers line having means associated therewith controlled by the operation of the substation set to disconnect the normal source of talking current from the said line, and to connect therewith an indicating instrument to show the magnitude of the foreign potential.

7. In a signaling system, the combination with a telephone subscribers line adapted to have a potential impressed thereon from a source normally foreign to the said subscribers line, a testing circuit inserted in the said subscribers line having means associated therewith controlled by the operation of the substation set to disconnect the normal source of talking current from said line, means to connect an indicating device across the said line and means to bridge a resistance across the line relay of the said subscribers line circuit, whereby the line lamp associated therewith may be operated.

In testimony whereof I have signed my name to this specification this 4th day of January, 1921.

WILLIAM H. MARTIN.

i fo 

